The next generation of coherent transceivers are extremely small requiring novel approaches to accommodate the small space available. For example, a Quad Small Form Factor Pluggable-Double Density (QSFP-DD) is as small as a finger and integrates an Application Specific Integrated Circuit (ASIC), a coherent receiver and transmitter, and a tunable laser. There is practically no room left for amplifying the signal after the modulation. Silicon photonics is well suited for these very compact optical systems but lacks the technology or capacity to amplify the signal intrinsically. There is a need for a very compact and integrated solution into the transmitter function to provide the signal with enough power to achieve the reach required, such as by a QSFP-DD.
Multiple research centers and companies have published papers over the years on heterogeneous and homogeneous integration of optical amplification chips and material onto silicon photonics, including lasers, Semiconductor Optical Amplifiers (SOA) with evanescent coupling, Indium phosphide (InP) growth, and the like. However, there has not been a solution to properly amplify coherent transmitters on-chip that has been demonstrated in production and can be used in a non-hermetic environment. Current solutions include various types of bonding the SOA with evanescent coupling, which is difficult and impractical in production due to high tolerances. Evanescent coupling is difficult to achieve in production due the very high manufacturing precision required. Some other techniques have been presented with side coupling, but lack the precision to have a doubled sided coupling required by the SOA to be inserted into a waveguide path with sufficient precision to achieve passive alignment. Others have presented coupling lasers in the cavity with passive or active alignment or presenting a full non-hermetic solution that achieves a non-hermetic, passively aligned SOA integration into a waveguide path.
There is no known solution that meets the need for on-chip amplification into a waveguide path while using passive alignment assembly equipment for passively aligned SOA integration into a waveguide path and that also provides a non-hermetic approach. Further, all previous solutions do not solve the end to end tolerancing problems to ensure proper and efficient coupling in and out of the chip.